Optical disks (storage media) such as CDs (Compact Disk) and DVDs (Digital Versatile Disk) are widely used to store digital information such as music information, video information, computer information, and the like. Further, with advent of a further information society, these storage media are strongly required to have higher density and larger volumes.
Further, in the optical disk, it is possible to make the storage density higher (it is possible to improve the storage capacity in each unit area) by reducing a beam spot diameter obtained from the optical pickup. A minimum diameter of the beam spot diameter is generally in proportion to λ/NA (λ represents a wavelength of a light source used, and NA represents an aperture of an optical system) due to optical diffraction. Thus, in order to improve the storage capacity, a wavelength of a light source used is made shorter, or an aperture of an optical system of the optical pickup is made larger. It is known that the improvement of the storage capacity is realized by performing these operations.
Further, a technique in which the wavelength of the light source used is made shorter has been being made practicable by using, for example, a blue-like semiconductor laser as a light-source semiconductor laser.
Further, as a method for making the aperture of the optical system of the optical pickup larger, for example, Patent Document 1 proposes a technique in which a pair of two objective lenses is used. By using the pair of two objective lenses, it is possible to set the aperture of the optical system to 0.8 or more, so that the storage density of the optical disk can be made higher.
However, such pair of two objective lenses is required to have high accuracy in formation of each lens. Further, as to each of the two objective lenses, due to limit in terms of a formable lens shape, a working distance between a surface of the optical disk and the objective lens is extremely small such as 0.1 mm to not more than 0.3 mm. Thus, in case of using the two objective lenses, when control error (referred to as servo deviation) occurs in driving the objective lens for example, it is difficult to avoid contact between the objective lens and the optical disk. Thus, a technique is proposed in which: a protector section formed by coating or the like is provided on an end portion of a protruding portion provided on a lens holder. According to the proposed technique, the objective lens is prevented from being directly in contact with the optical disk and the protector section is in contact with the optical disk, so that it is possible to protect the objective lens and the optical disk.
Incidentally, in an optical pickup device having a conventional objective lens driving device, when any vibration or impulse is exerted with no optical disk installed into the optical pickup device, the objective lens driving device's movable section whose one side is held by an elastic support section moves. In case where strong vibration or impulse is exerted, the elastic support section which holds the movable section may be deformed.
In case where the elastic support section is deformed, when the optical disk is installed therein, a relative position of the optical disk and the objective lens provided on the movable section changes from an initial position, so that a property of the objective lens driving device may be deteriorated.
Thus, in order to solve the foregoing problem, it is necessary to prevent the deformation of the elastic support section by restricting a movable range of the movable section of the objective lens driving device by means of any stopper mechanism or the like.
Further, as a specific example of an arrangement for preventing the deformation of the elastic support section, Patent Document 2 discloses an arrangement in which: as to an optical pickup having an objective lens driving device, a cover for covering an objective lens is provided on a housing so as to be positioned on the side where the optical disk is installed. Further, in the arrangement disclosed by Patent Document 2, a movable range of a movable section of the objective lens driving device in a vertical direction (hereinafter, referred to as a focusing direction) with respect to the optical disk is restricted by bringing the cover and the movable section of the objective lens driving device into contact with each other.
As another example thereof, Patent Document 3 discloses an arrangement in which a shock absorbing member is provided on a base section 15 for movably supporting an objective lens holder. More specifically, Patent Document 3 discloses an arrangement in which: a shock absorbing member is provided on an upper end portion of a yoke member of a magnetic circuit which has been inserted into a hole of the objective lens holder. Further, according to the arrangement of Patent Document 3, when the objective lens holder is driven in a focusing direction beyond a predetermined movable range, the objective lens holder comes into contact with an undersurface of the shock absorbing member, so that its movable range is restricted.
Note that, according to the arrangements of Patent Documents 2 and 3, a working distance between a surface of the optical disk and the objective lens is large (specifically 1 mm to 1.2 mm for example), so that it is possible to provide a cover or a shock absorbing member, which restricts a movable range of the objective lens holder in a focusing direction, between the surface of the optical disk and the objective lens.
[Patent Document 1]
Japanese Unexamined Patent Publication No. 123410/1998 (Tokukaihei 10-123410)(Publication date: May 15, 1998) (corresponding to U.S. Pat. No. 6,058,095)
[Patent Document 2]
Japanese Unexamined Patent Publication No. 28510/1993 (Tokukaihei 5-28510)(Publication date: Feb. 5, 1993) (corresponding to U.S. Pat. No. 5,453,881)
[Patent Document 3]
Japanese Unexamined Patent Publication No. 225588/1993 (Tokukaihei 5-225588)(Publication date: Sep. 3, 1993)
However, each of the conventional arrangements is such that: a restricting member for controlling the movable range of the movable section is formed between the surface of the optical disk and the objective lens, so that such arrangement raises such problem that: this is not applicable to an objective lens driving device for a high-density optical disk whose working distance is small (0.1 mm to 0.3 mm for example).
Specifically, for example, the arrangement of Patent Document 2 raises the following problem. The cover is provided on the housing of the optical pickup having the objective lens driving device. Thus, when an orientation of the objective lens driving device is adjusted with respect to the housing, a positional relationship between the cover and the objective lens driving device changes every time the objective lens driving device is set, so that it is difficult to stably restrict a movable range in which the movable section moves toward the optical disk in the focusing direction.
Further, in the objective lens driving device for a high-density optical disk for example, a high servo band is required, so that it is necessary to raise a rigidity of the whole movable section including the objective lens holder. However, when the rigidity of the movable section is raised, it is difficult to provide a hole, which allows a yoke member to be inserted, on the objective lens holder, so that it is difficult to provide the yoke member on the magnetic circuit. Thus, according to the arrangement of Patent Document 3 in which the shock absorbing member is provided on the upper end portion of the yoke member, it is extremely difficult to apply such arrangement to the objective lens driving device for a high-density optical disk.